The present invention relates to an amplifier circuit. More particularly, the invention relates to push-pull amplifiers using bipolar transistors.
It is necessary in an amplifier to minimize distortion in the output therefrom. A large variety of distortion reducing techniques have been proposed. According to one well-known technique, distortion is reduced by the use of AC negative feedback. In this case, however, the amplification factor is unavoidably reduced. Therefore, in order to obtain a desired amplification factor, an increased number of amplifying elements or stages is required. Further, the stability of the overall amplifier circuit is reduced with the use of this technique.
More specifically, transistors commonly used as amplifying elements have somewhat non-linear input/output characteristics. In view of this disadvantage, it has been proposed to employ a large amount of AC negative feedback. However, the use of a large amount of negative feedback does not adequately compensate for the non-linearities.
Further, in ordinary push-pull amplifiers using bipolar transistors, generally, two voltage sources, one positive and the other negative, are used. Accordingly, it is necessary to always maintain the potential level at the output terminal of the amplifier at a neutral level between the positive level and the negative level, that is, at ground level.
If a DC voltage were present at the output terminal, a DC current could flow through the load, such as a loudspeaker connected to the output terminal, resulting in damage to the loudspeaker.